Conventionally, various lighting devices (light irradiation device) have been developed to carry out an inspection of a surface of a work. For example, an annular-shaped lighting device that irradiates light of a low angle from its circumference, a line-shaped lighting device that irradiates line light on a work, or other lighting device that meets various aspects of a work or various purposes of irradiating light have been known as the lighting devices as shown in Japan Patent laid open 1.
Especially, a line-shaped lighting device of a converging type is so arranged that bullet-shaped LEDs are laid out in a line and a cylindrical lens is arranged in front of the bullet-shaped LEDs so as to irradiate thin line-shaped light on a work.    Japan Patent laid open 1 number: 10-21729